1. Field of the Invention
Embodiments of the present invention generally relate to high speed network interfaces, and more particularly to gigabit Ethernet using the 1000Base-T standard.
2. Description of the Related Art
One of the more recent developments in high speed networking has been gigabit Ethernet (GbE) as defined in the IEEE 802.3ab standard, also known as 1000Base-T. Able to provide 1 gigabit per second (Gbps) bandwidth in addition to the simplicity of an Ethernet connection, GbE offers a smooth, seamless upgrade path for current 10Base-T or 100Base-T Ethernet installations running at 10 megabits per second (Mbps) and 100 Mbps, respectively.
In order to obtain the requisite gigabit performance levels, GbE transceivers are interconnected using four separate pairs of twisted Category 5 (Cat 5) copper wires for a single link. In reality, gigabit Ethernet requires Category 5 Enhanced (Cat 5e) cables, but since virtually all cables sold as Cat 5 meet the Cat 5e standard, this specification will simply refer to Cat 5 cable from now on. Getting back to the four twisted wire pairs, gigabit communication, in practice, involves the simultaneous, parallel transmission of these four information signals, with each signal conveying information at a bit rate of 250 Mbps, followed by their simultaneous, parallel reception and concatenation. The present 1000Base-T standard also requires that the digital information being processed for transmission be symbolically represented in accordance with a five-level pulse amplitude modulation scheme (PAM5) and encoded with an 8-state Trellis coding methodology. The 2-bit PAM5 scheme actually limits the transmission across the Cat 5 cable to 125 Mbaud, using approximately 80 MHz of the cable bandwidth.
Despite the increased bandwidth of gigabit Ethernet, the need for four twisted pair wires for a single 1000Base-T link causes problems, especially when compared to only two pairs of twisted wires needed for the previous 10Base-T and 100Base-T standards. Furthermore, network switching integrated circuits (ICs) have grown in capacity faster than physical link elements (e.g. network cables and connectors), and thus, the switching capacity of linecards has outpaced faceplate densities. Because of this, the data switch on the linecard will be undersubscribed, and the unused bandwidth of the network IC will be wasted whenever the faceplate jacks on such a limited density linecard run out.
Accordingly, what is needed is a gigabit Ethernet system that achieves greater connection density, preferably while still working within the boundaries of existing GbE standards and cabling, while maintaining backwards compatibility.